The invention relates to hook-and-loop fasteners, their manufacture, and products incorporating such fasteners.
Presently, it is known to use hook-and-loop fasteners on disposable absorbent garments, e.g., diapers and other similar garments, to secure the garment in place upon the body. Although the fasteners work quite well for their intended purpose, they tend to cause irritation to the flesh, especially when used next to babies' tender skin.
It is known to reduce the abrasiveness and tendency to scratch of hook tapes by reducing the stiffness, or flex modulus, of the polymer used to mold the tapes. In doing so, however, the hooks become ineffective because they, too, lose their stiffness and hence their ability to resist the forces required to hold a disposable absorbent garment in place.
Currently, the molded plastic hook fastener components used on disposable absorbent garments have a nominal base thickness of about 0.012 inches. The hooks are molded using a method like that disclosed in Fischer, U.S. Pat. No. 4,794,028, incorporated by reference, in which molten polymeric resin is introduced between a molding roller and a pressure-applying means which forces the resin into the hook-shaped cavities and allows for the formation of a base to which the hooks are integrally joined.
Because the base of the fastener component is quite thin, it is notch-sensitive. In other words, during use, the base is susceptible to tearing in the lengthwise direction, with the tear propagating between and parallel to the rows of hooks, when the base is notched or nicked by even slight tearing, or by sewing or otherwise securing the fastener to some other product.
To reduce this notch-sensitivity, so-called rip-stops have been integrally molded with the base of the fastener. These are typically of hump- or bump-form and lie in the spaces between rows of hooks. The rip-stops, which reduce notch-sensitivity by providing localized thickening of the base of the fastener, typically extend between and are integrally molded with the hooks in adjacent rows as well as the base.
For efficiency, the hook fastener components are produced in the form of wide intermediary tapes on the order of twelve to eighteen inches wide. These "wide-width tapes" have "selvedges" or blank spaces extending lengthwise along the tape at selected places across the width where eventual separation is desired. The selvedges are spaced apart by widths corresponding to the desired width of the final hook tape, e.g., half an inch to an inch with, for example, on the order of twenty to forty lengthwise rows of hooks between selvedges. The wide-width tape is subsequently split along the selvedges to separate it into individual hook tapes of the desired width. The individual hook tapes so produced will then have blank selvedge areas along either side that are half as wide as the selvedges running along the wide-width tape.
Splitting has been facilitated by molding splitting channels into the base of the fastener along the centers of the selvedges. As taught in Fischer, the molding roller is composed of an alternating stack of molding rings, which have hook-shaped cavities cut into their peripheries, and spacer rings. Unlike the spacer rings disclosed in Fischer which have flat peripheral edges, however, the spacer rings used when making hook tapes with rip-stops have hump-shaped indentations cut into their peripheries to form the rip-stops. The splitting channels are formed by splitting rings--a third type of ring incorporated into the stack of rings--that are thin and have a slightly larger diameter than the molding rings and spacer rings. The splitting rings have had rounded, "bullet-shaped" edges. These rings typically have been nominally on the order of 0.008 inches thick, with their overall diameter and the diameter of their edges selected such that the base of the fastener is reduced to the order of 0.002 inches thick at the bottom, center of the splitting channel.
A wide intermediary tape is split into the individual, final tapes by manually tearing the end of the wide-width tape a limited distance along each of the splitting channels to form leading ends of individual hook tapes, threading the leading ends through the fingers of a splitting comb, and pulling the tape past the fingers of the splitting comb. Because the splitting channel causes a localized weakness in the base of the fastener, the wide intermediary tape continues to split along the splitting channels as it is pulled continuously through the splitting comb. Alternatively, a splitting blade can be used instead of a splitting comb. The leading tape ends are alternately laced over the blade or under the blade and the wide intermediary tape is pulled past the blade, the blade continuously splitting it along the length of the splitting channels to produce the individual tapes.
Unfortunately, however, although this method of forming the individual narrow tapes is highly efficient, the edges of the individual tape have remained stiff and sharp and tend to produce the above noted skin irritation.